It has heretofore been proposed, as evidenced by U.S. Pat. No. 3,426,623, to provide an overdrive device for a motor vehicle, which includes a stationary housing; an input drive shaft; an output drive shaft; an epicyclic gear train comprising a sun gear journaled upon the input shaft, a planetary gear device meshing with the sun gear and fixed for rotation with the input shaft and a ring gear device meshing with the planetary gear device and fixed for rotation with the output shaft; and means for selectively fixing the sun gear to the planetary gear device to cause rotation thereof with the input shaft and to the stationary housing to prevent rotation thereof with the input shaft, whereby to provide direct drive and overdrive connections between the input and output shafts, respectively. More specifically, this prior type of overdrive device employs a control member in the form of a collar, which is spline connected to the sun gear for relative axial movement alternatively into sun gear locking engagement with axially spaced toothed couplings carried on the planetary gear device and the stationary housing. Coupling of the collar with these toothed couplings is facilitated by employing a pair of synchronizer rings arranged one in association with each of such toothed couplings.
A drawback of prior overdrive devices of the type employing an epicyclic gear train is that the sun gear and control member must be accelerated/decelerated between rotational speeds of zero and that speed corresponding to rotational speed of the input shaft each time a change is made in the connection between the input and output shafts.